Computers that are able to process data and/or pieces of information circulating in a communications network used in a secured communication system, for example a railway management system are known. In order to ensure critical security functions required by the railway management system, the probability of occurrence of a wrong and undetectable datum at the output of such a computer should be reduced as much as possible. The European Railway Safety standard EN 50 128 for example imposes that equipment related to the safety of trains be designed so that their probability of failure on demand is comprised between 10−9 and 10−7. A known technique for ensuring safety is called <<composite security>> and consists of having the same processing operations performed by several data processing modules of a same computer, and then of proceeding with a <<majority vote>>. For this purpose, each module computes an output datum from a same input datum. Moreover, such a computer generally includes arbitration means capable of ensuring the <<majority vote>> function among the computed output data.
The arbitration means of such a computer however include a minimal hardware layer, sometimes completed with a software layer. Now, the failure of such a hardware layer may cause a security flaw which may lead to critical incidents for the security communication system.